"Ten years ago the infant mortality rate for babies hand-reared in Wolong's nursery was 100 percent," Don Lindburg says. When a wild female panda gives birth to twins, she typically cares for one and abandons the other to die. For twins born in captivity, human caretakers would try to save the rejected newborn, but almost always failed. "Those cubs were getting a dog-milk formula," Lindburg says, until a San Diego Zoo nutritionist came up with a replacement formula that more closely mimics the high-fat milk nursing pandas get from their mothers.

Wolong staff also boosted their survival rate by "twin swapping," which alternates babies between mother's care and nursery tending. Even though pandas don't usually raise two offspring at once, new mothers seem willing to accept both cubs—with a little help from human nannies.

Conservation International biologist Lü Zhi says the popular notion that giant pandas are naturally poor breeders is just wrong. Recent studies show that wild pandas reproduce about as robustly as North American brown bears: On average, a wild female will have a cub every other year for some 15 years, adding five to six new pandas to the population over her lifetime.

Years of frustrating captive-breeding failures turn out to be mostly the result of human mismanagement, zoo staff acknowledge—making 2005's successes even more gratifying. Two cubs born in the U.S. boosted the year's total count, as did a surviving baby in Japan, and cubs produced at breeding centers in China's Sichuan and Shaanxi Provinces.

All those cubs pushed the captive population closer to a magic number: 300. With that many pandas, says population biologist Jon Ballou, "we can have a self-sustaining captive population, and maintain 90 percent of known giant panda genetic variation for a century." A member of the Conservation Breeding Specialist Group, Ballou compiles a list every year that rates the genetic desirability of potential matings between all the captive adult pandas in the world.

So cuddly, funny, rambunctious, adorable Tai Shan turns out to be more than just the fulfillment of the National Zoo's decades-long dream of raising a healthy giant panda cub, more than a crowd-pleasing, four-legged rock star in a black-and-white bear suit. He stands for the possibility of genuine international cooperation on behalf of endangered animals, for the powers of science to turn substantial, long-term funding into real progress on tough conservation challenges. And like every one of the cubs that swelled the giant panda ranks last year, he moves his species one step closer to a self-sustaining captive population, and one step back from the brink of extinction. Pretty heady stuff for a one-year-old. Happy birthday, Tai Shan.